Abstract
Weeds are an important part of the spontaneous plant biodiversity of vineyards and their management represents a major lever for the agroecological transition. The objective of this thesis is to understand the response of weed communities to management practices (chemical weeding, tillage, mowing), at different spatial and temporal scales, and to explore their influences on organic matter recycling processes (decomposition, microbial activity related to nitrogen cycle), using trait-based approach. For this purpose, we mobilized several networks of French vineyards (Champagne, Rhone Valley, Bordeaux and Occitanie), including a historical network in the Montpellier region set up in 1978. We show that chemical weed control, applied consecutively for at least five years, favors weed communities with resource-conserving foliar strategies, with low decomposition potential, whereas tillage and mowing favor weed communities with acquisitive foliar strategies, with high decomposition potential. Herbicides promote acquisitive and soil exploring root strategies while mowing and tillage are associated with weed communities with ‘out-sourcing' strategies which relies on collaboration with mycorrhizal fungi. Weed communities with root exploration strategies are associated with a higher abundance of nitrifying microorganisms. In 40 years (1980s to present), climate change (+2°C summer temperature) has induced more stress-tolerant weed communities, while diversification of management practices has favored less competitive communities. Current weed communities are 41% more abundant and 24% richer than 40 years ago, reflecting their resilience to changes in climate and practice. The thesis shows that the practice of mowing is particularly promising. After five years, mowing promotes highly decomposable weed communities with high biomass and nitrogen content, approximately twice the microbial biomass of soils under other management practices, and promotes twice the number of weed species than under other management practices. This thesis demonstrates that weed management is an undeniable lever for driving the diverse and functional weed communities of tomorrow.